(NDK) Added explicit initialisation

Components and systems just can't be initialized at startup, so we need
some kind of explicit initialisation. I followed the same layout as the
others modules by adding a core class (Ndk::Sdk) which will initialize
components and systems, and Nazara's modules.

This is starting to get serious, I like it.


Former-commit-id: 263500e8d16db70ef7f92047b8a7e3235c08bcd0

SDK/include/NDK/Sdk.inl

@@ -0,0 +1,11 @@
+// Copyright (C) 2015 Jérôme Leclercq
+// This file is part of the "Nazara Development Kit"
+// For conditions of distribution and use, see copyright notice in Prerequesites.hpp
+
+namespace Ndk
+{
+	inline bool Sdk::IsInitialized()
+	{
+		return s_referenceCounter != 0;
+	}
+}